ACTA BOT. VENEZ. 33 (1): 103-117. 2010 103 MORPHOLOGY AND ANATOMY OF FLOWERS OF DALECHAMPIA STIPULACEA MÜLL.ARG. (EUPHORBIACEAE) Morfología y anatomía de flores deDalechampia stipulacea Müll.Arg. (Euphorbiaceae) Luiz Antonio DE SOUZA, Aparecido Caetano DA SILVA e Ismar Sebastião MOSCHETA Universidade Estadual de Maringá, Departamento de Biologia, Avenida Colombo, 5790, Maringá, Paraná, Brasil [email protected] RESUMEN Las flores de Dalechampia han sido reportadas como modelo para los estudios de evolución floral. Sin embargo, la literatura registra escasos estudios sobre la anatomía floral de estas plantas. El análisis estructural de las inflorescencias y flores deDalechampia stipu- lacea es el objetivo del trabajo. El pseudanto consiste en inflorescencias masculinas y feme- ninas con dos brácteas grandes y flores monoclamídeas. En la inflorescencia masculina hay una glándula resinosa. En las brácteas y flores se encuentran tricomas no glandulares, trico- mas glandulares y glándulas. Las brácteas y el perianto no presentan parénquima en empa- lizada. La antera es tetrasporangiada con la pared formada por epidermis, endotecio, capa media y tapete secretor. En el ovario se observaron dos meristemas, el adaxial con origen epidérmico y otro intermedio proveniente del mesófilo. El óvulo es anátropo, bitegumenta- do y crasinucelar. El estilo tiene el tejido transmisor central con una hendidura reducida. Los resultados anatómicos obtenidos son comparados con las flores e inflorescencias de otras especies del género y discutidos en relación con la ecología de la polinización. Palabras clave: Bráctea, Dalechampia, Euphorbiaceae, flor femenina, flor masculina, pe- rigonio, pseudanto ABSTRACT The flowers ofDalechampia species have been reported as a model for the study of floral evolution. However, the literature does not record floral anatomical studies of these plants. The structural analyses of inflorescences and flowers of Dalechampia stipulacea was the objective of this paper. The pseudanthium consists of male and female inflorescenc- es with two large bracts and monochlamydeous flowers. In the male inflorescence there is a resinous gland. In the bracts and flowers occurred nonglandular, glandular trichomes and glandular emergencies. The bracts and perianth without palisade parenchyma. The anther is tetrasporangiate with wall formed by epidermis, endothecium, middle layer and secretory tapetum. In the ovary wall meristematic regions were observed in the epidermis and meso- phyll regions. The ovule is anatropous, bitegmic and crassinucellate. The style has central transmitting tissue with a reduced rift. The obtained anatomical results are compared with flowers of other species of the genus and discussed in relation to pollination ecology. Key words: Bract, Dalechampia, Euphorbiaceae, female flower, male flower, perigone, pseudanthium ISSN 0084-5906 Depósito Legal 196902DF68 Recibido: 03/12/2008 Aceptado: 30/11/2009 104 De Souza, Da Silva and Moscheta INTRODUCTION The neotropical species of Dalechampia Plum. ex L. (Euphorbiaceae) con- stitute a model system for the study of floral evolution. This system was chosen because it comprises a tractable number of closely related species exhibiting con- siderable variation in pollination ecology. The pseudanthia of most Dalecham- pia species secrete a triterpene resin that is collected by bees that use resin in nest construction. The resin-reward system apparently evolved by modification of preexisting resin-secretion system that defended the flowers from herbivores (Armbruster 1996). Most of the Dalechampia species are also noteworthy for the presence of stinging trichomes in the flowers and other plant organs, for which they are com- monly called “pó-de-mico”, “cipó-urtiga”, “urtiga” and “urtiga-de-boi”. The pseu- danthium inflorescence that occurs in the genus is also considered unique among Euphorbiaceae (Maia et al. 2002). The flower morphology ofDalechampia species has been presented in sev- eral investigations of taxonomic nature, in pollination studies or floral biology (Graner 1942; Capinpin & Bruce 1955; Webster & Webster 1972; Armbruster & Webster 1979; Armbruster 1996; Sazima et al. 1985; Armbruster et al. 1992; Frei- tas et al. 2001; Silva et al. 2001; Maia et al. 2002). Anatomical studies of flowers of Euphorbiaceae are scarce, but include notably studies of: Manihot utilissima Pohl (Manihot esculenta Crantz) microsporogenesis and megasporogenesis (Gra- ner 1935); ontogenetic and structural analysis of the Manihot utilissima flowers (calyx, stamen and gynoecium) (Toledo 1963); ovule integuments, chalaza and vascularization of Crotonoideae, Euphorbioideae and Acalyphoideae (Tokuoka & Tobe 1998, 2002, 2003); and Croton sarcopetalus Müll.Arg. floral and extrafloral nectaries (Freitas et al. 2001). Therefore, the present investigation has as objec- tive the morphological and anatomical analysis of the Dalechampia stipulacea Müll.Arg. inflorescence which is a liana that occurs at high frequency in forest remnants of the Parana, Brazil. MATERIAL AND METHODS Inflorescences of two Dalechampia stipulacea were collected at the forest remnant (“Bosque dos Pioneiros”), in Maringa, Brazil (state of Parana). Voucher materials were deposited at the UEM Herbarium, collection number: K.S. Mourão 11720 and L.A. Souza 11746. Morphological analyses of the inflorescences, flowers and floral buds were conducted with fresh and fixed material. The terminology used here follows that of Sazima et al. (1985), Weberling (1992), Armbruster (1996) and Maia et al. (2002). The Foster’s (1950) clearing technique was used for study of venation pattern in the bracts. The terminology of venation pattern was based on Hickey (1979). Anatomical preparations of inflorescences were made from fixed material Morphology and anatomy of Dalechampia flowers 105 in FAA (formalin, acetic acid, ethanol), dehydrated through alcohol series, em- bedded in hydroxymethacrylate (Gerrits 1991), sectioned via rotary microtome (cross- and longitudinal sections), and stained following the toluidine blue 0,05% in phosphate buffer pH 4,7 technique (O’Brien et al. 1964). Photomicrographs were prepared using an Olympus BX50 optical micro- scope and Nova Optical Systems stereoscope fitted with a digital Canon Power Shot A95 camera and subsequently prepared using software Zoom Browser EX 4.6. RESULTS AND DISCUSSION Inflorescence and flower morphology The monoecious plant of D. stipulacea possesses a pseudanthium inflores- cence with two white or yellow-greenish bracts which subtend the staminate and pistillate cymes. Bracts are ovate with round and slightly cordate bases, and 3, 4-lobed apices (Fig. 1a). The bracts have actinodromous venation with seven pri- mary veins (five thick and two fine veins) diverging radially from a single point; the veins have basal position and marginal development (Fig. 1a). The bracts have trichomes and stalked glands. In Dalechampia the inflorescence is a bilaterally symmetrical pseudanthi- um, a unique configuration within the Euphorbiaceae. The sequence of changes in color and position of the bracts during inflorescence development reflects suc- cessive adaptation to protection of flowers (before anthesis), to attraction of pol- linators (at anthesis) and to protection of capsules (after anthesis) (Webster & Webster 1972). The male inflorescence (Fig. 1b, d) was considered by Sazimaet al. (1985) as a pleiochasium. It has six pedicellate, monochlamydeous flowers with green sepaloid perianth, an androphore and numerous stamens (Fig. 1c). The anthers are bithecate and rimose. The inflorescences presented two small, obovate and pilose bracts. The male inflorescence includes a laminar gland (Fig. 1b) which exudes a highly sticky compound. Armbruster & Webster (1979) recorded that this gland complex in Dalechampia secretes resin as a reward for insect visits. Only female bees of Euglossa melanotricha, Apidae, Euglossini, are attracted to the D. stipula- cea inflorescences, where they gather resin; these euglossine bee species are con- sidered as the most effective pollinator in D. stipulacea (Sazima et al. 1985). The female cyme inflorescence (Fig. 1b, d) consists of three flowers with two short, obovate, pilose and white bracts. The pistillate flowers are monochlamydeous with green perianth, trilobate and pilose ovary, long pilose style, and clavate stigma with a central cavity. The perianth possesses trichomes and stalked glands. Inflorescence and flower anatomy The pseudanthium presents nonglandular and glandular trichomes, and glands in the bracts and flowers (Fig. 2). Nonglandular trichomes are unicellular, 106 De Souza, Da Silva and Moscheta b gl a sg mb c d ap pe fb Fig. 1. Inflorescence morphology of Dalechampia stipulacea. a. Bract. b. Inflorescence in superior view. c. Male flower.d. Inflorescence in lateral view. ap = androphore; fb = bract of the female flower; gl = gland; mb = male floral bud; pe = perianth; sg = stigma. Scales = 1 cm (a), 7 mm (b), 3 mm (c) and 2 mm (d). thick-walled and pointed (Fig. 2a). Unicellular glandular trichomes (Fig. 2c) oc- cur sparsely on the perianth; these trichomes have wide bases and pointed extrem- ities; the literature does not record unicellular glandular trichomes for Dalecham- pia. Pluricellular glandular trichomes (Fig. 2b) present a central cell armed with a sharp-pointed crystal, surrounded by several epidermal jacket-cells. Pluricellular glandular trichomes of D. stipulacea are similar to the stinging hairs of Tragia (Thurston 1976) and Dalechampia scandens